a) Field of the Invention
The present invention relates to low dielectric constant film materials, and to low dielectric constant films and semiconductor devices using such materials.
b) Description of the Related Art
Higher integration and higher speed of semiconductor integrated circuits are desired. A signal transmission speed in a semiconductor integrated circuit is restricted by wiring resistance and parasitic capacitance between wiring lines. Wiring resistance and parasitic capacitance are increasing as the wiring width and pitch are becoming narrow because of higher integration of semiconductor integrated circuits. Although parasitic capacitance can be reduced by thinning wiring lines, wiring resistance increases and the reduced capacitance does not contribute to improving the signal transmission speed. In order to increase the signal transmission speed, it is effective to make an inter-level insulating film have a low dielectric constant.
Conventionally, an inter-level insulating film is made of non-organic material such as silicon dioxide (SiO2), silicon nitride (SiN), silicon oxyfluoride (SiOF) and phosphosilicate glass (PSG), or organic polymer such as polyimide. A relative dielectric constant of a silicon dioxide film formed by chemical vapor deposition (CVD) is about 4. A relative dielectric constant of a SiOF film is about 3.3 to 3.5 which is lower than that of silicon dioxide. However, since SiOF has a high moisture absorption rate, a SiOF film is likely to absorb moisture and raise its relative dielectric constant.
As low dielectric constant materials, attention has been paid to siloxane resin having Si—H bonds, porous siloxane resin or the like.
As siloxane resin is washed with alkaline solution, SiOH having a high moisture absorption rate is produced because of hydrolysis. Therefore, siloxane resin washed with alkaline solution raises its relative dielectric constant. Apart from this, an organic polymer film has as low a glass transition temperature as about 200 to 350° C. and a high thermal expansion coefficient. Damages to wiring layers are therefore large.